Melt the butter in a saucepan over low heat. Add the flour, and stir it with a wooden spoon or spatula for around 3 minutes, until the roux is frothy and the taste of raw flour is gone. Meanwhile, heat the milk in another pan. Add the warm milk gradually to the roux, stirring hard all the while. Turn up the heat and cook, stirring, until the sauce is just at the boiling point. Turn down the heat and let it simmer for a few minutes. Now add the pepper and Tabasco. Don’t be afraid of the Tabasco: it will help to bring out the taste of the cheese. Stir in the heavy cream or crème fraîche and simmer a little longer, until the flavors are blended.

Cook and drain the macaroni.

Mix three-quarters of the grated cheese into the simmering sauce. As soon as it melts, combine it with the drained macaroni, and pour it into a baking pan. Sprinkle the top with the remaining cheese, and bake for 20 to 30 minutes in a 350° oven